Postoperative pulmonary complications, the most common of which are atelectasis and pneumonia, are due largely to the pathophysiological effects on the lungs of anaesthesia and surgery as well as preexisting disease, in particular chronic obstructive airways disease (COAD).

The otherwise safe and useful anaesthetic halothane has been suspected of producing the occasional complication of hepatic necrosis, ascribed either to a drug allergy or to biotransformation to reactive intermediates. Several characteristics, such as middle age, obesity and multiple administrations of the anaesthetic, seem to put the patient at higher risk.